1. Field of the Invention
The apparatus of the present invention relates to data processing communication systems, and more particularly to the automatic switching of defective modules to operative modules when a defective communication path is sensed.
2. Description of the Prior Art
Communication systems may include a network of input/output terminals which communicate via leased or circuit switched communication lines. Topologies of terminals is point-to-point, multipoint or clusters controllers exist. The communication lines may be terminated by MODEMs. Information from a terminal may be transmitted into a communication network and information to the terminal may be received by the terminal from the communication network by a MODEM.
A site, such as a Department store, may have many terminals connected to the communication network by a number of MODEMs. These MODEMs may be installed at a central site for ease of connection to the communication site and for ease of maintenance. An installation is usually organized such that a bank of MODEMs may handle a group of terminals.
In the event that a MODEM at the CSU is defective, arrangements are usually available to switch the terminal or group of terminals to another MODEM. This switching of MODEMs was normally accomplished by operator or maintenance personnel manually patching lines into spare MODEMs.
Many terminals at a site requiring many MODEMs, particularly if MODEMs having different functionality are required, are normally located in a single area. Those MODEMs are typically rack mounted requiring a large number of cables, making MODEM replacement difficult and prone to error.
These prior art systems had usually operated as dual systems. When one system was inoperative there was either manual switching to a back-up system, or there was a simplified automatic system for switching systems. That is, a test signal sent into one system would cause automatic switching to the back-up system if the test signal were not received by a terminating unit.